Positive displacement compressors have a pulsed output as trapped volumes are delivered to discharge. Mufflers are normally provided to reduce the noise generated as a result of the gas pulsations. When the compressor is initially shut off, there is a pressure differential across the compressor that tends to equalize through the compressor rather than through the refrigeration or air conditioning system. To prevent the reverse operation of the compressor as an expander without load, a check valve is normally provided in the compressor discharge to prevent reverse flow and operation. It is often a problem locating the check valve in an appropriate location and, if the valve is biased closed, it may move responsive to the pulsed output and thereby contribute further noise.